The invention is directed to a process for the production of mixed granulates of carbon black and light fillers in a spiked screw granulator and the product produced as well as rubber compositions containing such product.
Carbon black or light fillters are used for reinforcing natural or synthetic rubber. To simplify the addition to rubber mixtures there are also used mixtures of carbon black and light fillers, so-called "black-white mixtures". These "black-white mixtures" for example exhibit good industrial rubber properties in the production of vehicle tires. Especially good industrial rubber properties are obtained in rubber articles which are subject to a dynamic load. With the use of black-white mixtures besides it is possible to produce a high degree of filling whereby the properties of the filled polymers depending on the mixing ratios can be influenced positively in the manner aimed at.
However, there are certain difficulties in the addition of both fillers in the form of a so-called black-white mixture to the rubber mixture because during the addition of the fillers with a fixed mixing ratio from the supply bunker to the rolls or in the kneader there always exists the danger of a dissociation into the components and therewith an inexact dosaging.
It is known for better handling and for avoiding an inexact dosaging of the black-white mixture of carbon black and light filler to produce mixed granulates made of both components by mixing dry, non-pelleted carbon black into a filler cake dough of a precipitated filler until there is formed the highest possible homogeneous composition using granulating apparatus, as e.g. distributor rolls, solid rolls or drum granulators, granulating and drying (Steenken German AS No. 11 46 606 and related Steenken U.S. Pat. No. 3,203,819).
However, this process has the disadvantage that the mixed granulates obtained are shaped irregularly, relatively coarse, have poor flowability and therewith are inexactly dosageable.
The known process according to German AS No. 11 46 606 and the related Steenken U.S. patent furthermore has the disadvantage that the production of a homogeneous and definite combined mixture is only possible batchwise and with considerable apparatus and energy expense because the aqueous, pasty filter cake of precipitated filler to be mixed with the carbon black in the filter press accumulates in the form of irregular shaped, coarse lumps. The true granulation can only be carried out subsequently in a second step.
From Rothbuhr German OS No. 15 92 861 there is known a process with which powdery carbon black and air dried, powdery precipitated silica is wet shaped in a special apparatus into pellets with water which contains an adhesive and subsequently the granulate formed is dried.
Disadvantages of the known process are shown from the fact that it is only possible to granulate batchwise in special apparatus and furthermore that there is required a partial double drying of the silica. There is also known from Rothbuhr German OS No. 15 92 861 a further process which uses a spiked screw granulator.
However, it is explained in Rothbuhr German OS No. 15 92 861 that customarily used pin containing screw granulators for the production of carbon black pellets are not suited for the production of mixed granulates.
Therefore there is a need for a regular shaped, pellet shaped mixed granulate having good flowability and good dosageability produced according to a continuous, energy saving process with known apparatus.